Phase change memory device in which a phase change layer is stably formed and prevented from lifting and method for manufacturing the same

ABSTRACT

A phase change memory device includes a semiconductor substrate having a plurality of phase change cell regions; a lower electrode formed in each of the phase change cell regions on the semiconductor substrate; an insulation layer formed on the semiconductor substrate to cover the lower electrode and defined with a contact hole which exposes the lower electrode; a heater formed in the contact hole; a conductive pattern formed on the insulation layer to be spaced apart from the heater; a phase change layer formed on the heater, the conductive pattern, and portions of the insulation layer between the heater and the conductive pattern; and an upper electrode formed on the phase change layer. This phase change memory device allows the phase change layer to be stably formed and prevents the phase change layer from lifting

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Korean patent applicationnumber 10-2006-0113470 filed on Nov. 16, 2006, which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a phase change memory device and amethod for manufacturing the same, and more particularly, to a phasechange memory device in which a phase change layer is stably formed andis prevented from lifting, and a method for manufacturing the same.

In general, memory devices are largely divided into a volatile RAM(random access memory), which loses inputted information when power isinterrupted, and a non-volatile ROM (read-only memory), which cancontinuously maintain the stored state of inputted information even whenpower is interrupted.

When considering volatile RAM, a DRAM (dynamic RAM) and an SRAM (staticRAM) can be mentioned, and when considering non-volatile ROM, a flashmemory device such as an EEPROM (electrically erasable and programmableROM) can be mentioned.

As is well known in the art, while the DRAM is an excellent memorydevice, the DRAM must have high charge storing capacity, and to thisend, since the surface area of an electrode must be increased, it isdifficult to accomplish a high level of integration. Further, in theflash memory device, due to the fact that two gates are stacked on eachother, a high operation voltage is required when compared to a sourcevoltage. Accordingly, a separate booster circuit is needed to form thevoltage necessary for write and delete operations, making it difficultto accomplish a high level of integration.

To improve upon the current memory devices, researches have beenactively making an effort to develop a novel memory device that has asimple configuration and is capable of accomplishing a high level ofintegration while retaining the characteristics of the non-volatilememory device. A phase change is memory device recently disclosed in theart is a product of this effort.

In the phase change memory device, a phase change, which occurs in aphase change layer interposed between a lower electrode and an upperelectrode, from a crystalline state to an amorphous state is due tocurrent flow between the lower electrode and the upper electrode. Theinformation stored in a cell is recognized by the medium of a differencein resistance between the crystalline state and the amorphous state. Indetail, in the phase change memory device, a chalcogenide layer, being acompound layer made of germanium (Ge), stibium (Sb), and tellurium (Te),is employed as a phase change layer. As a current is applied, the phasechange layer undergoes a phase change by heat, that is, Joule heat,between the amorphous state and the crystalline state. Accordingly, inthe phase change memory device, when considering the fact that thespecific resistance of the phase change layer in the amorphous state ishigher than the specific resistance of the phase change layer in thecrystalline state, in a read mode, whether the information stored in aphase change cell has a logic value of ‘1’ or ‘0’ is determined bysensing the current flowing through the phase change layer.

It is known that, since the phase change memory device has a simplestructure, and adjoining cells do not interfere with each other, a highlevel of integration is possible. Also, since the phase change memorydevice has a read speed of several tens of ns (nano second) and arelatively high write speed of several tens to several hundreds ns, highspeed operation is possible.

Additionally, because the phase change memory device has excellentapplicability to the conventional CMOS logic processes allowingmanufacturing costs to be reduced, the phase change memory device isregarded as a memory device that is highly advantageous in terms ofcommercialization.

However, when considering phase change memory devices of the prior art,in the course of depositing a phase change material, that is, in thecourse of depositing a phase change material layer on an insulationlayer, the phase change material layer is likely to be poorly depositedon the insulation layer, and even if the phase change material layer isdeposited, when conducting subsequent processes lifting of a phasechange layer is likely to occur.

SUMMARY OF THE INVENTION

An embodiment of the present invention is directed to a phase changememory device in which a phase change layer is stably formed and isprevented from lifting, and a method for manufacturing the same.

In one aspect, a phase change memory device comprises a semiconductorsubstrate having a plurality of phase change cell regions; a lowerelectrode formed in each of the phase change cell regions on thesemiconductor substrate; an insulation layer formed over thesemiconductor substrate to cover the lower electrode, the insulationlayer having a contact hole which exposes the lower electrode; a heaterformed in the contact hole; a conductive pattern formed on theinsulation layer except the heater and portions of the insulation layersurrounding the heater; a phase change layer formed on the heater, theconductive pattern, and portions of the insulation layer between theheater and the conductive pattern; and an upper electrode formed on thephase change layer.

The heater is can be formed to completely fill the contact hole or to berecessed on a surface thereof.

The phase change layer and the upper electrode are formed in the shapeof a pattern in each phase change cell region or in a manner such thatthe phase change cell regions are connected with one another.

In another embodiment, a method for manufacturing a phase change memorydevice comprises the steps of forming a lower electrode in each phasechange cell region on a semiconductor substrate; forming an insulationlayer over the semiconductor substrate to cover the lower electrode;defining a contact hole by etching the insulation layer to expose thelower electrode; depositing a conductive layer on the insulation layerwhereby the contact hole is filled; etching the conductive layer, andthereby forming a heater in the contact hole and a conductive pattern,while exposeing the heater and portions of the insulation layer on bothsides of the heater; depositing a phase change material layer and aconductive layer for an upper electrode on: the exposed heater, theinsulation layer and the conductive pattern; and etching the conductivelayer ,the phase change material layer, and the conductive pattern,thereby forming a phase change layer and an upper electrode on theheater, the portions of the insulation layer on both sides of theheater, and the conductive pattern.

The conductive layer is deposited through CVD or ALD.

The conductive layer is made of any one of a titanium nitride layer, atitanium tungsten layer, and a titanium aluminum layer.

The heater may be formed to completely fill the contact hole or to berecessed on a surface thereof.

The phase change layer and the upper electrode are formed in the shapeof a pattern in each phase change cell region or in a manner such thatthe phase change cell regions are connected with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a phase change memorydevice in accordance with an embodiment of the present invention.

FIGS. 2A through 2E are cross-sectional views illustrating process stepsof a method for manufacturing a phase change memory device in accordancewith another embodiment of the present invention.

FIGS. 3A through 3E are cross-sectional views illustrating process stepsof a method for manufacturing a phase change memory device in accordancewith still another embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 is a cross-sectional view illustrating a phase change memorydevice in accordance with an embodiment of the present invention.

Referring to FIG. 1, a phase change memory device in accordance with anembodiment of the present invention includes: a semiconductor substrate110, which has a plurality of phase change cell regions; a lowerelectrode 130, which is formed in each of the phase change cell regionson the semiconductor substrate 110; an insulation layer 140, which isboth formed on the semiconductor substrate 110 to cover the lowerelectrode 130 and m also has a contact hole exposing the lower electrode130; a heater 150, which is formed in the contact hole; a conductivepattern 160, which is formed on the insulation layer 140 and is spacedapart from the heater 150; a phase change layer 170 which is formed onthe heater 150, the conductive pattern 160, and portions of theinsulation layer 140 between the heater 150 and the conductive pattern160; and an upper electrode 180, which is formed on the phase changelayer 170.

The unexplained reference numeral 120 designates an oxide layer.

In the present invention; due to the fact that the phase change layer170 is formed on the heater 150, the conductive pattern 160, and theportions of the insulation layer 140 between the heater 150 and theconductive pattern 160; the phase change layer 170 can be stably formedand is prevented from lifting. That is to say, due to the presence ofthe conductive pattern 160 formed on the insulation layer 140, the phasechange layer 170 is stably formed and is prevented from lifting.

FIGS. 2A through 2E are cross-sectional views illustrating process stepsof a method for manufacturing a phase change memory device in accordancewith another embodiment of the present invention.

Referring to FIG. 2A, semiconductor substrate 210 has a plurality ofphase change cell regions. A lower electrode 230 is formed in each ofthe phase change cell regions on the semiconductor substrate 210. Aninsulation layer 240 is deposited on the semiconductor substrate 210 tocover the lower electrode 230. The insulation layer 240 is etched toform a contact hole H exposing the lower electrode 230. The unexplainedreference numeral 220 designates an oxide layer.

Referring to FIG. 2B, a conductive layer is deposited on the insulationlayer 240 in such a way as to fill the contact hole H. The conductivelayer is formed through CVD (chemical vapor deposition) or ALD (atomiclayer deposition), and is made of any one of a titanium nitride layer(TiN layer), a titanium tungsten layer (TiW layer), and a titaniumaluminum layer (TiAl layer). By etching the conductive layer, a heater250 is formed in the contact hole H and a conductive pattern 260 isformed. The heater 250 and portions of the insulation layer 240 on bothsides of the heater 250 are left exposed by the etching process. Theheater 250 is formed in such a way as to completely fill the contacthole H.

Referring to FIG. 2C, a phase change material layer 270L and aconductive layer 280L for an upper electrode are deposited on theexposed heater 250, the exposed portions of the insulation layer 240,and the conductive pattern 260. In the present invention, when the phasechange material layer 270L is depositing, the presence of the conductivepattern 260 allows for stable deposition, and it also prevents a phasechange layer from lifting in subsequent processes.

In the conventional art, when the phase change material layer isdeposited on the insulation layer, the phase change material layer islikely to be poorly deposited on the insulation layer, and the depositedphase change material layer will likely be lifted is during subsequentprocesses. However, in the present invention, when etching theconductive layer to form the heater in the contact hole, since theconductive pattern is formed on the insulation layer, the phase changematerial layer can be stably deposited due to the presence of theconductive pattern, and it is possible to prevent the phase change layerfrom lifting when conducting subsequent processes. Further, because theconductive pattern and the heater are spaced apart when formed, theoccurrence of a short circuit is prevented when depositing the phasechange material layer.

Referring to FIG. 2D, by etching the conductive layer 280L for an upperelectrode, the phase change material layer 270L, and the conductivepattern 260; a phase change layer 270 and an upper electrode 280 areformed on: the heater 250, portions of the insulation layer 240 on bothsides of the heater 250, and the conductive pattern 260.

At this time, the phase change layer 270 and the upper electrode 280 canbe formed in each phase change cell, or they can be formed in a mannersuch that the plurality of phase change cells are connected with oneanother as shown in FIG. 2E.

In the present invention, when the phase change layer and the upperelectrode are formed in a manner such that the plurality of phase changecells are connected with one another, it is possible to solve theproblem caused by the fact that, as the size of the cell is decreased,and the etched size of the upper electrode and the phase change layer isalso decreased, a phase change does not stably occur due to thevariation of a composition resulting from the etch loss of the phasechange layer on the edge thereof.

FIGS. 3A through 3E are cross-sectional views illustrating process stepsof a method for manufacturing a phase change memory device in accordancewith yet another embodiment of the present invention.

Referring to FIG. 3A, Semiconductor substrate 310 has a plurality ofphase change cell regions. A lower electrode 330 is formed in each ofthe phase change cell regions on the semiconductor substrate 310. Aninsulation layer 340 is deposited over the semiconductor substrate 310to cover the lower electrode 330. By etching the insulation layer 340, acontact hole H exposing the lower electrode 330 is defined. Theunexplained reference numeral 320 designates an oxide layer.

Referring to FIG. 3B, a conductive layer is deposited on the insulationlayer 340 filling the contact hole H during the deposition. Theconductive layer is formed through CVD (chemical vapor deposition) orALD (atomic layer deposition), and is made of any one of a titaniumnitride layer (TiN layer), a titanium tungsten layer (TiW layer), and atitanium aluminum layer (TiAl layer). By etching the conductive layer, aheater 350 is formed in the contact hole H and a conductive pattern 360is formed. The heater 350 and portions of the insulation layer 340 onboth sides of the heater 350 is are left exposed by the etching process.When etching the conductive layer, the heater 350 is formed in such away as to be recessed to some extent form the surface of the insulationlayer.

Referring to FIG. 3C, a phase change material layer 370L and aconductive layer 380L for an upper electrode are deposited on theexposed heater 350, the exposed portions of the insulation layer 340,and the conductive pattern 360. In the present invention, the phasechange material layer is formed on the exposed recessed heater, and muchof the heat is generated in the center portion of the phase changematerial layer, which has relatively low heat conductivity. It istherefore possible to minimize heat loss, which was typically caused byheat dissipated through the (upper and lower) electrodes made ofmetallic materials that had relatively high heat conductivity.Therefore, when comparing the present invention to the conventional cellstructure, a reset current can be reduced by 50% or more.

Referring to FIG. 3D, by etching the conductive layer 380L for an upperelectrode, the phase change material layer 370L, and the conductivepattern 360, a phase change layer 370 and an upper electrode 380 areformed on: the heater 350, the portions of the insulation layer 340 onboth sides of the heater 350, and the conductive pattern 360.

At this time, the phase change layer 370 and the upper electrode 380 canbe formed in each phase change cell, or can be formed in a manner suchthat the plurality of phase change cells are connected with one anotheras shown in FIG. 3E.

Thereafter, while not shown in the drawings, by sequentiallyimplementing a series of subsequent well-known processes, themanufacture of a phase change memory device according to the presentinvention is completed.

As is apparent from the above description, in the present invention whenforming the heater in a contact hole, by forming a conductive pattern onan insulation layer using the same material as the heater, a phasechange material layer can be stably deposited due to the presence of theconductive pattern, and it is possible to prevent a lifting phenomenonfrom occurring in a phase change layer.

Although a specific embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and the spirit of theinvention as disclosed in the accompanying claims.

1. A method for manufacturing a phase change memory device, comprisingthe steps of: forming a lower electrode on a semiconductor substratecontaining a plurality of phase change cell regions, the lower electrodebeing formed in each phase change cell region; forming an insulationlayer over the semiconductor substrate to cover the lower electrode;defining a contact hole by etching the insulation layer to expose thelower electrode; depositing a conductive layer on the insulation layer,during which the contact hole is filled; etching the conductive layer,such that a heater is formed in is the contact hole and a conductivepattern is formed on the insulation layer, and the heater and portionsof the insulation layer on both sides of the heater are exposed;depositing a phase change material layer and a conductive layer for anupper electrode on the exposed heater, the insulation layer, and theconductive pattern; and etching the conductive layer, the phase changematerial layer, and the conductive pattern, such that a phase changelayer and an upper electrode are formed on the heater, the portions ofthe insulation layer on both sides of the heater, and the conductivepattern.
 2. The method according to claim 1, wherein the conductivelayer is deposited through CVD or ALD.
 3. The method according to claim1, wherein the conductive layer is made of any one of a titanium nitridelayer, a titanium tungsten layer, and a titanium aluminum layer.
 4. Themethod according to claim 1, wherein the heater is formed to completelyfill the contact hole.
 5. The method according to claim 1, wherein theheater is is formed to be recessed on a surface thereof.
 6. The methodaccording to claim 1, wherein the phase change layer and the upperelectrode are formed in the shape of a pattern in each phase change cellregion.
 7. The method according to claim 1, wherein the phase changelayer and the upper electrode are formed in a manner such that the eachphase change cell region is connected with one another.